When pipe repairs are to be carried out, three main repair scenarios are normally encountered. This will include (i) pipes subject to external metal loss (caused by corrosion or mechanical damage), (ii) pipes subject to internal metal loss (caused by corrosion, erosion or erosion/corrosion) and (iii) piping components that are leaking. In addition to these main repair scenarios, the extent of the deterioration or damage (i.e. localized or extensive) has also to be considered when choosing the repair methods and repair components.
Current repair methods include clamps (localized repairs) and specialized connectors with sleeves (extensive repairs). It is equally possible to encircle the defective area with close fit metallic sleeves which are welded together. This, however, has to be seal welded. These methods could cause weld induced damage or material property changes on the pipe being repaired. In underwater conditions this may require specialist habitats to carry out hyperbaric welding. This can prove costly and can pose additional dangers. Welding on live pipelines poses further additional dangers.
Condition and extent of damage of the pipe essentially dictates the type of repairs to be carried out. If the external surface is damaged to the extent that an elastomeric seal cannot provide sufficient sealing forces in the immediate vicinity of the damage, or in the relatively unaffected areas adjacent to the major damage (these areas being used to effect the sealing forces of ‘stand’-off repair clamps), the external pipe surface may need to be re-installed using some form of filler material. Developments using epoxy-filled steel sleeves have been shown to accommodate such areas of extensive damage and have applications for a whole range of defects including corrosion, non-propagating cracks, dents or gouges in both axial and circumferential orientation, and girth weld associated anamolies. The epoxy-filled sleeve repair technique is typically recommended on areas operating below 100 barg with temperatures not exceeding 100° C. It was assumed that epoxy filled sleeves can be used for leak containment. However in various tests conducted it has been found that the sleeves were only able to contain leaks below 40 barg. Additional tests were conducted to determine if pumping epoxy and allowing it to cure under pressure i.e. in equilibrium pressure (to that within the pipe) would produce better results. The tests prove that higher pressures are obtained but in practical terms this will involve derating the pipe or suspending production and could prove costly for operators. There is a need therefore to develop a method where the pipes can be repaired without derating the pipe or suspending the throughput of the pipe.
The prior art method is expensive in that heavy duty connectors dimensioned to fit the damaged pipes, need to be provided. Such connectors are expensive and take substantial man-hours to design, manufacture and assemble. The prior art composite fibre wraps which has a pressure limit not exceeding 40 barg. When the axial pressure exceeds 40 barg or when used in isolation are considered temporary repairs.